Page:The New International Encyclopædia 1st ed. v. 07.djvu/813

* FLIGHT. 729 FLIGHTLESS BIRDS. to the size of the species, the small hats flutter- ing, the large fruit-hats Sapping their wings somewhat like a crow. The Length and narrow- ness of the wings of pterodactyls, and the small surface for muscular attachment, indicate that these creatures sailed or flew with infrequent wing-strokes, after the fashion of a chimney- swift. Relation of Size and Weight to Flight. It is an interesting question whether or not the ani- mals that lly represent the limits of size and weight attainable by living creatures. The al- batross, condor, swan, and pterodactyl represent the maximum of weight, but these range only from 15 to 30 pounds, and the spread of wings is but 7 feet in the swan, 8 to 10 feet in tin- condor, and 10 to 14 feet in the albatross. The very largest examples of pterodactyls had a spread of wing of 20 feet; but owing to the small size of the body and wonderful lightness of the skeleton, their weight at the outside was not more than 30 pounds. These reptiles, with their great expanse of wing, offer one of the excep- tions to the general rule that the wing area per pound is proportionally less in large Hying ani- mals than in small, a seeming anomaly which, though imperfectly understood, is partly based on the fact that the great sweep of a large wing makes it much more effective than one of small dimensions. Very erroneous ideas prevail both as to the power of the muscles and the speed attained by birds. Marey long ago showed that the contractile power of the muscular fibres was certainly no greater in birds than in mammals, and observation has shown that even ducks, which fly very rapidly, seldom attain a greater speed than 35 to 40 miles an hour, although under favorable conditions some species may exceed this. ft has long been evident that if the problem of artificial flight is solved it will be by a system of planes imitating the methods employed in sailing flight, and all recent experiments have been conducted on this line. But while there have been many different theories to explain the principle of soaring or sailing, many of them fanciful and some based on misinterpretations of facts, the subject is far from being under- stood, although the researches of Langley, Maxim, Chanute, and Lilienthal have thrown much light upon it. Flight of Bikds. So long ago as 1680 an Italian, Borelli, propounded a theory of flight which in its essential feature holds good to-day. Noting that all wings are rigid in front, flexible behind, he considered that as the wings were raised and lowered they formed obliquely directed planes alternately facing backward and forward, by which the bird was, so to speak, wedged through the air. More recently Professor Petti- grew, of England, and Professor Marey, of France, have studied the flight of birds, the latter in par- ticular devoting much attention to the subject, and devising very elaborate experiments to ascer- tain the action of the wings. Professor Marey was able to photograph the position of the wing at different phases of the stroke. This shows that the wing is not merely moved up and down, but that it has a variety of movements by which, combined with the resistance of the air, the wing assumes a somewhat twisted shape. According to Marey, the movements of the wing in a pigeon are briefly as follows: At the commencement of the downward stroke the wings arc spread to the utmo I and brought downward and forward until thei) tips - advance of the head. Ai the beginning of flight the downward a at the wing lips touch, while on thei] they strike above the bird's back, producing the clap ping sound so noticeable when pi i Lake flight. The wing is una rai ed rapidly and at thi tone Bexed at the wrist-joint, to be again straightened as the wings are raised to their full extent. In performing these motions the long axis of the wing describes an ellipse, bein ried first forward and downward, then backward and upward. During the downward stroke the front edge of the wing look, downward, the under surface of the wing being directed backward, these posit ions being exactly reversed during the upward stroke. It will be seen thai by this de- position the wing has a propelling force during the downward stroke, while during the recovery, or upward movement, it acts as an inclined plane to raise the bird. There is, nevertheless, a rising and falling of the body, more or less pronounced, at every stroke, so that the forward path of the bird is not a perfectly straight line. Professor Pettigrew insists that during the downward st roke of the wing its under surface is directed forioard, and that the long axis of the wing describes a figure oo at each stroke, and that the wing, by this screw-like action, acts much after the fashion of a propeller; but the results obtained by photography do not seem to hear out this theory. The method of sailing flight is less easily ex- plained, because the results obtained seem out of all proportion to the force expended. Having obtained its initial velocity, the bird is held to avail itself of every increase or upward eddy of the wind to rise, although in doing this onward movement is checked. The bird then sails for- ward and downward, to again rise and repeat these movements. Soaring, or ascending in spi- rals, is performed by this method, aided by up- ward currents of air. The difficulty in the way of this theory is that birds progress for long distances almost horizontally, while we cannot suppose that convenient upward currents are everywhere to be met with. But the experiments of Lilienthal have shown how little force is necessary for gliding flight, since by jumping from an elevation he was able, with the aid of wings of his invention, to sail for upward of a quarter of a mile. For power of long-distance flight, see Migration of Animals. Bibliography. Pettigrew, Animal Locomotion (London, 1873) ; Marey, Animal Mechanics (Lon- don, 1874) ; Marey, Le vol. Physioloaie du motive- ment du vol. des oiseaux (Paris, 1890) : Newton, article "Flight," in Dictionary of Birds (Lon- don, 1893-96) ; Headlev, The Structure and Life of Birds (London, 1895). FLIGHT INTO EGYPT, The. A painting by Murillo, representing the Virgin riding on an ass, and contemplating the sleeping Child. It is in the possession of the Duchesse de Gal'.iera, Paris. FLIGHTLESS BIRDS. Certain groups and species of birds lack the power of flight. Such birds fall into two categories: (1) ratite birds; and (2) groups or isolated species among cari- nate birds distinguished from their fellows by this disability. The ratite birds (see Rathve)